1. Field of the Invention
The field of the present invention relates generally to flexible shaft couplings, more particularly to bellows style flexible shaft couplings, and most specifically to bellows style flexible shaft couplings further possessing an elastomeric covering.
2. Discussion of the Prior Art
Bellows style flexible shaft couplings are considered to be well known in the art. The annular convolutions of a relatively thin sheet of metal formed into a generally cylindrical shape provide torsional rigidity and longitudinal flexibility. Angular misalignments of up to half a degree are accommodated. U.S. Pat. No. 3,232,076 issued Feb. 1, 1966 to Sundt is an example. Torsional wind-up, i.e. backlash, is considered a problem with increased torsional load.
Rubber or elastomer sleeve shaft connectors are also known. U.S. Pat. No. 2,170,627 issued Aug. 22, 1939 to Berryman, U.S. Pat. No. 2,171,999 issued Sep. 5, 1939 to Weiland and U.S. Pat. No. 2,195,993 issued to Morrill are examples, respectively, of uniform cylindrical, medially enlarged, and medially concave configurations. Vulcanized rubber elements attached at either end to metal shaft bosses generally characterize these couplings. Rubber boots disposed loosely about, i.e. spaced apart from, metal shaft couplings are also well known.
U.S. Pat. No. 3,621,674 issued Nov. 23, 1971 to Ulics and Wheatley discloses a bellows style flexible shaft coupling encased in a molded rubber sleeve in combination with a Cardan style ball joint held in an elastomer socket for the purpose of reducing velocity fluctuations in the latter. U.S. Pat. No. 3,623,339 issued Nov. 30, 1971 to Muller discloses use of two concentrically disposed bellows having elastomer therebetween for the purpose of increasing torsional rigidity and decreasing torsional wind-up. U.S. Pat. No. 3,747,367 issued Jul. 24, 1973 to Muller discloses an improvement in this dual bellows style coupling wherein elastomer is injected between the two thereby alleviating the need for removal of an internal core necessary in molding of the elastomer intermediary layer.
Molding rubber about generally cylindrical bellows style flexible shaft couplings having annular convolutions has been shown to reduce torsional wind-up. Molding rubber about a metal bellows requires a complex pressurized molding however which is an expensive process. Injection of elastomer in between concentrically disposed bellows is simpler and hence less expensive than this type of molding but it still requires pressurization in addition to the use of two bellows instead of one.
In addition to torsional wind-up it is noted that the resonant frequency of a bellows type shaft coupling presents problems at relatively large rotational speeds, i.e. above 3,000 revolutions per minute (rpm), and metal fatigue results which, unchecked, rapidly leads to catastrophic failure, i.e breaking, in common language. Operation is hence effectively limited to the rotational velocity at which resonant frequency obtains. For relatively small shaft couplings, i.e. less than one inch diameter, operating at relatively high speeds this is considered, quite logically, to be a much greater problem than torsional wind-up.
A need is hence discerned for a means of reducing the stress experienced by bellows style flexible shaft couplings during resonant frequency, for extending the operational life and increasing the maximum operational velocity of bellows style flexible shaft couplings, without the expense associated with molding an elastomer about the metal bellows in a pressurized manufacturing operation.
Objects of the Invention
The encompassing object of the present invention is the enhancement of operational characteristics of a bellows style flexible shaft coupling possessing a single layer metal bellows of generally cylindrical shape without the expense of molding an elastomer about the same.
A principal object of the present invention is to prolong the operational life of a bellows style flexible shaft coupling possessing a single layer metal bellows of generally cylindrical shape without the expense of molding an elastomer about the same.
An ancillary object of the present invention is reducing the duration of resonant frequency experienced by a bellows style flexible shaft coupling possessing a single layer metal bellows of generally cylindrical shape without the expense of molding an elastomer about the same.
Another principal object of the present invention is to increase the maximum operational rotational velocity of a bellows style flexible shaft coupling possessing a single layer metal bellows of generally cylindrical shape without the expense of molding an elastomer about the same.
Another ancillary object of the present invention is increasing the rotational velocity resulting in resonant frequency being experienced by a bellows style flexible shaft coupling possessing a single layer metal bellows of generally cylindrical shape without the expense of molding an elastomer about the same.
Principles Relating to the Present Invention
In achievement of the above stated objects it is suggested that a substantially cylindrical rubber sleeve be disposed about the bellows of a single bellows style flexible shaft coupling without the use of pressurization. A rubber sleeve can be molded to the desired configuration separately from the metal bellows and fitted about the same under ambient conditions. Molding the rubber sleeve alone is much less complicated and hence less expensive than molding the same about the bellows. The rubber sleeve is not bonded to the metal bellows and torsional rigidity is hence unimproved but the rotational velocity at which resonant frequency is encountered is generally increased thereby increasing the maximum operational speed of the coupling. The duration of resonant frequency, moreover, is reduced by a factor of five which results in a commensurate increase in operational life at speeds exceeding the rotational velocity resulting in resonant frequency.
After fitting the rubber sleeve about the bellows appropriate application of heat melts the rubber and adheres the same to the metal bellows without the need for and expense of molding the sleeve about the bellows. The duration of resonant frequency is reduced by a factor often, resulting in a commensurate increase in operational life at speeds exceeding the rotational velocity resulting in resonant frequency, and torsional rigidity is increased thereby reducing torsional wind-up as well. The rubber sleeve can also be applied in a dip molding operation under ambient conditions.
The very considerable expense associated with a compound molding of elastomer about the metal bellows is avoided and both the operational life and maximum operational speed are increased largely owing to the unexpectedly large reduction in the duration of resonant frequency obtained by the dampening of vibration provided by a simple cylindrical rubber sleeve disposed about the metal bellows.
Other benefits and advantages of an embodiment in accordance with the principles relating to the present invention may be appreciated with a reading of the detailed discussion of the preferred embodiment following especially if conducted with reference to the drawings attached hereto and briefly described immediately below.